In the field of magnetic heads to be mounted on a magnetic recording device such as a hard disk drive (HDD), recently, perpendicular recording method has become a predominant recording method in order to improve recording density with respect to a magnetic recording medium such as a hard disk. The perpendicular recording method provides not only a high linear recording density but also an advantage that the recording medium after recording is less influenced by thermal fluctuation.
In order to improve the recording capacity of a hard disk drive (HDD), however, it is required not only to improve the recording resolution by increasing the coercive force of a medium but also to increase the track density by narrowing the width of a perpendicular writing main magnetic pole film of a perpendicular recording magnetic head. Since the width of the main magnetic pole film is decreased with an increase in the recording density, when increasing the recording density, it is extremely important to control the width of the main magnetic pole film as accurately as possible from the viewpoint of increasing the yield of the magnetic head.
For instance, the technique as disclosed in US2006/0238918A1 has been widely known as a method for forming the main magnetic pole film. This prior art document discloses a technique that an inorganic insulating layer is formed on a magnetic layer, a resist mask material is formed on the inorganic insulating layer, and ion milling is performed in this state to obtain a main magnetic pole of an inverted trapezoidal shape.
In this prior art, since the resist mask material defines the trailing side width (track width) of the main magnetic pole, the width of the mask material has to be accurately transferred to the trailing side width (track width) of the main magnetic pole. However, since the inorganic insulating layer lies between the resist mask material and the magnetic layer that will be formed into the main magnetic pole, the width of the resist mask material is firstly transferred to the inorganic insulating layer and the width of the inorganic insulating layer is then reflected on the magnetic layer that will be formed into the main magnetic pole, so that it is difficult to accurately transfer the width of the resist mask material to the trailing side width (track width) of the main magnetic pole. Particularly when the inorganic insulating layer is thick, the mask formed of the inorganic insulating layer by ion milling has a dominantly trapezoidal shape with almost the same width as the resist mask material at its top side in contact with the resist mask material but with an increased width at its bottom side in contact with the magnetic layer. Accordingly, it is difficult to accurately transfer the width of the resist mask material to the trailing side width (track width) of the main magnetic pole.
Since the above-described problem occurs when disposing a mask of an inorganic insulating material on a material to be dry etched, disposing a resist mask material on the mask for dimensioning the planar area of the material to be dry etched, and then performing milling, it does not pertain only to the perpendicular recording magnetic head. Also in integrated circuits and other electronic component elements, it cannot be avoided as long as adopting the above-mentioned mask structure for milling.